Chemotherapy and radiation therapies are two current clinical modalities commonly used for the treatment of cancer. Mostly these techniques are effective to block the growth of a tumor; however, there is often a recurrence of the disease, possibly because of incomplete cell killing or cells acquiring drug resistance.
Glucocorticoid receptor is a nuclear hormone receptor residing in various cells including both cancerous and non-cancerous cells. It has two subtypes alpha and beta. This receptor, a ligand activated transcription factor, upon activation translocates itself into the nucleus. As a homodimer it binds to specific DNA sequences called glucocorticoid response elements (GRE) and positively or negatively regulates transcription of target genes.
Dexamethasone (dex), a potent glucocorticoid acts on intracellular glucocorticoid receptor and regulates transcription of several genes. Several of the glucocorticoids including dex exhibit antiproliferative effect on several tissues of different origin (Corroyer et. al. 1997; Ramalingam et. al. 1997; Rider et. al. 1996; Goya et. al. 1993; Wattenberg and Estensen 1996). These molecules also regulate and control metabolism, development, inflammation, cell growth, proliferation and differentiation (Yamamoto et. al. 1985; Cole et. al. 1995; Rogatsky et al. 1997). In various cancer cells such as in non-small cell lung carcinoma Dex mediates suppression of cellular proliferation through the accumulation of cells in G1/G0 stage of the cell cycle and by hypophosphorylation of retinoblastoma protein (Greenberg et. al. 2002). Glucocorticoid-signaling through glucocorticoid receptors potentiate a possible hypoxia related pathway leading to inflammation. As an anti-inflammatory agent, dex also possesses an important role in inhibiting hypoxia inducible factor (HIF-1), which has direct role in mediating angiogenesis through up-regulation of VEGF (Leonard et. al 2005). Hence, glucocorticoids such as dexamethasone (dex) are a very important and inexpensive drug-like substitute used in various pathological conditions.
There is an example of dexamethasone being structurally modified into a cationic entity by conjugating spermine into it. The cationic dexamethsone-spermine compound is used to complex and transfer genes to airway epithelial with concurrent reduction of inflammation (Gruneich et. al. 2004).
The viral based gene delivery is quite well known and is extensively investigated utilizing their phenomenally efficient process of delivering genes to wide variety of cells. A number of problems including host toxicity, immunogenic responses and non-specific genomic integration of transferred gene make viral delivery a risky option for delivering genes. In comparison, non-viral gene delivery is a much more robust and clinically safe option compared to viral counterparts. The patented cationic lipid, DODEAC (Banerjee et. al. U.S. Pat. Nos. 6,503,945 and 6,436,516), whose structure is N,N-dihydroxyethyl, N,N-dioctadecyl, ammonium chloride forms cationic liposome using co-lipid cholesterol in membrane filtered water. This product has been used for the transfection of DNA into cultured eukaryotic cells of various origins. However, the formulation in spite of exhibiting moderate transfection of genes to all cells irrespective of origin shows no specific targeting of genes to cancer cells expressing glucocorticoid receptor. Towards this end, the present invention relates to development of a new dexamethasone carrying cationic lipid based formulation, which targets and deliver genes to glucocorticoid receptor expressing cancer cells.
Therefore, keeping in view the hitherto known prior art, the inventors of the present invention realized that there exists a need to develop an aqueous formulation useful for selective targeting and delivering gene to cancer cells, comprising a cationic lipid, a steroid and a neutral co-lipid.
The present invention deals with targeted gene delivery which is specific to glucocorticoid receptors of cancer cells only and not of normal cells. The normal cells may be having glucocorticoid receptors but the formulation of the present invention will not target the gene to those normal cells.